diff --git a/mysql-test/r/analyze_format_json.result b/mysql-test/r/analyze_format_json.result
index 2c339042f43..461dd35ef87 100644
--- a/mysql-test/r/analyze_format_json.result
+++ b/mysql-test/r/analyze_format_json.result
@@ -143,6 +143,7 @@ ANALYZE
         "attached_condition": "(tbl2.b < 60)"
       },
       "buffer_type": "flat",
+      "buffer_size": "128Kb",
       "join_type": "BNL",
       "r_filtered": 100
     }
@@ -180,6 +181,7 @@ ANALYZE
         "attached_condition": "(tbl2.b < 60)"
       },
       "buffer_type": "flat",
+      "buffer_size": "128Kb",
       "join_type": "BNL",
       "attached_condition": "(tbl1.c > tbl2.c)",
       "r_filtered": 15.833
diff --git a/mysql-test/r/explain_json.result b/mysql-test/r/explain_json.result
index 93220cb5fd7..65582912c93 100644
--- a/mysql-test/r/explain_json.result
+++ b/mysql-test/r/explain_json.result
@@ -365,6 +365,7 @@ EXPLAIN
         "attached_condition": "(tbl2.b < 5)"
       },
       "buffer_type": "flat",
+      "buffer_size": "128Kb",
       "join_type": "BNL",
       "attached_condition": "(tbl2.a = tbl1.a)"
     }
@@ -618,6 +619,7 @@ EXPLAIN
         "filtered": 100
       },
       "buffer_type": "flat",
+      "buffer_size": "128Kb",
       "join_type": "BNL"
     }
   }
@@ -651,6 +653,7 @@ EXPLAIN
         "first_match": "t2"
       },
       "buffer_type": "flat",
+      "buffer_size": "128Kb",
       "join_type": "BNL",
       "attached_condition": "((t1.b = t2.b) and (t1.a = t2.a))"
     }
@@ -687,6 +690,7 @@ EXPLAIN
           "filtered": 100
         },
         "buffer_type": "flat",
+        "buffer_size": "128Kb",
         "join_type": "BNL",
         "attached_condition": "((t1.b = t2.b) and (t1.a = t2.a))"
       }
@@ -799,6 +803,7 @@ EXPLAIN
               "filtered": 100
             },
             "buffer_type": "flat",
+            "buffer_size": "128Kb",
             "join_type": "BNL",
             "attached_condition": "((t2.b <> outer_t1.a) and trigcond(((<cache>(outer_t1.a) = t1.a) or isnull(t1.a))))"
           }
@@ -849,6 +854,7 @@ EXPLAIN
               "filtered": 100
             },
             "buffer_type": "flat",
+            "buffer_size": "128Kb",
             "join_type": "BNL",
             "attached_condition": "(tbl2.b = tbl1.b)"
           }
diff --git a/sql/my_json_writer.cc b/sql/my_json_writer.cc
index 7a3dc776093..e97db210da7 100644
--- a/sql/my_json_writer.cc
+++ b/sql/my_json_writer.cc
@@ -130,6 +130,27 @@ void Json_writer::add_ll(longlong val)
 }
 
 
+/* Add a memory size, printing in Kb, Kb, Gb if necessary */
+void Json_writer::add_size(longlong val)
+{
+  char buf[64];
+  if (val < 1024) 
+    my_snprintf(buf, sizeof(buf), "%ld", val);
+  else if (val < 1024*1024*16)
+  {
+    /* Values less than 16MB are specified in KB for precision */
+    size_t len= my_snprintf(buf, sizeof(buf), "%ld", val/1024);
+    strcpy(buf + len, "Kb");
+  }
+  else
+  {
+    size_t len= my_snprintf(buf, sizeof(buf), "%ld", val/(1024*1024));
+    strcpy(buf + len, "Mb");
+  }
+  add_str(buf);
+}
+
+
 void Json_writer::add_double(double val)
 {
   char buf[64];
diff --git a/sql/my_json_writer.h b/sql/my_json_writer.h
index 3a7defc3566..8ab20b10d73 100644
--- a/sql/my_json_writer.h
+++ b/sql/my_json_writer.h
@@ -108,6 +108,7 @@ public:
   void add_str(const String &str);
 
   void add_ll(longlong val);
+  void add_size(longlong val);
   void add_double(double val);
   void add_bool(bool val);
   void add_null();
diff --git a/sql/sql_explain.cc b/sql/sql_explain.cc
index 3fbb720e6c5..2f421a22c40 100644
--- a/sql/sql_explain.cc
+++ b/sql/sql_explain.cc
@@ -1360,6 +1360,7 @@ void Explain_table_access::print_explain_json(Explain_query *query,
     writer->end_object(); // "block-nl-join"
     writer->add_member("buffer_type").add_str(bka_type.incremental?
                                               "incremental":"flat");
+    writer->add_member("buffer_size").add_size(bka_type.join_buffer_size);
     writer->add_member("join_type").add_str(bka_type.join_alg);
     if (bka_type.mrr_type.length())
       writer->add_member("mrr_type").add_str(bka_type.mrr_type);
diff --git a/sql/sql_explain.h b/sql/sql_explain.h
index f4f421a76a4..aef4badf0e8 100644
--- a/sql/sql_explain.h
+++ b/sql/sql_explain.h
@@ -511,6 +511,8 @@ class EXPLAIN_BKA_TYPE
 public:
   EXPLAIN_BKA_TYPE() : join_alg(NULL) {}
 
+  size_t join_buffer_size;
+
   bool incremental;
 
   /* 
diff --git a/sql/sql_join_cache.cc b/sql/sql_join_cache.cc
index cec0755c9b0..23357ac871d 100644
--- a/sql/sql_join_cache.cc
+++ b/sql/sql_join_cache.cc
@@ -2582,6 +2582,8 @@ void JOIN_CACHE::save_explain_data(EXPLAIN_BKA_TYPE *explain)
 {
   explain->incremental= MY_TEST(prev_cache);
 
+  explain->join_buffer_size= get_join_buffer_size();
+
   switch (get_join_alg()) {
   case BNL_JOIN_ALG:
     explain->join_alg= "BNL";